Rubber die



Sept. 10, 1935. s c CLARK I 2,013,949

RUBBER DIE Filed March 5, 1931 INVENTOR Samuel 6'. Clark BY %l riaw ATTORNEYS Patented Sept. 10, 1935 UNITED STATES RUBBER DIE Samuel 0. Clark, Pontiac, Mich., assignor to Baldwin Rubber Company, a corporation of Michigan Application March 5, 1931, Serial No. 520,348

4 Claims.

My invention relates to dies and particularly to a method of constructing dies from a vulcanizable material.

When a thin sheet of metal, cardboard or like 6' materials is to be formed in relief or with embossed surfaces, it has been the practice in the past to place the sheet between two dies having oppositely disposed forming surfaces which when pressed together shape the sheet into the form 10 of the dies. The dies are usually made of steel or other hard metal,although some attempts have been made heretofore to construct such dies from composition materials. The dies so constructed have been more or less unsatisfactory because of 15' their short life.

In practicing my invention I employ a plurality of sheets of unvulcanized hard rubber material which is placed under a die having a forming surface and press the die and layers of rubber ma- 20 terial firmly together in a heating press wherein the sheets of rubber are-vulcanized into a hard homogeneous mass having a surface which is an exact opposite counterpart of the aforesaid die surface. A die so constructed is a mate of the 25 original die and has been found to have a life greater than that of any other composition die and at least as great as that of its mated. metal die member.

Accordingly, one object of my invention is to 30 1 provide a set of dies for embossing sheets of material, one of whichis constructed from a vulcanizable hard rubber material which is pressed into compact engagement with a forming surface .and vulcanized to provide a hard, resilient ngm- 35 her. r

Another object of my invention is to provide a set of dies of the above described type having the die which is made of vulcanizablematerial provided with a reinforcing screen or metal sheet'to 40 prevent the shrinking of the die'material.

A further object of my invention is to provide a set of dies of the above described type. which are economical of manufacture, which are constructed with a saving of time and labor, and which 45 have a length of life at least as great as dies heretofore employed for the same purpose.

Numerous other objects and features of novelty of my invention willbe either specifically pointed out or will become apparent when referring, for a better understanding of my invention, to the following description in conjunction with the accompanying drawing wherein: V

Figure 1 is a sectional view of a die and the embodying features of my invention,

Fig. 2 is a view of the structure shown in Fig. 1 with the die pressed into firm engagement with the material,

Fig. 3 is a reduced view similar to that of Figs. 1 p

Fig. 6 is a view of the structure shown in Fig.

5 with the die pressed firmly into engagement with the material.

Fig. 7 is an enlarged broken perspective view of a finished product after being formed in the die structures illustrated in Fig. 6.

Referring to Fig. 4, I have disclosed a sheet of cardboard Ill which has been formed to have a central embossed or relieved surface H which is formed thereon between a pair of dies l2 and i3. The metal dies heretofore constructed for forming the sheets were expensive, entailing considerable laborfor cutting the surfaces of the dies which registered with'ieach other andwere pro vided with the proper clearances. The steel dies were found to have considerable longevity and dies of other materials heretofore attempted to be substituted therefor, were found to be unsatisfactory because of their short life.

When a formable material is substituted for metal when constructing one member of the die set, considerable saving in labor and cost as well as time ensued, which effects a considerable advantage over the employment of two diesmade of metal. "Furthermore, the construction of a single die having the indented surface which con forms to the sh'apeof the raised surface of the finished product is considerablyche aper to-construct thani-ts mated die member having a surface of opposite contour. i For this reason an additional saving ensues when the cheaper die is the one constructed from metal and its more expensive mated member is formed therefrom by pressing the die into a moldable material, and the material hardened. The die member thus provided will have a surface of exact opposite contour to that of the metal die and will require only a slight machining of the mated male and female portions of one or both of the die elements to provide the proper clearance for the reception of the formable material therebetween. 5

Difiiculty had been experienced heretofore in providing the proper material for constructing such nioldable dies, the material usually being hard and brittle and for this reason easily chipped or powdered and an imperfectly formed product resulted. When the material was too soft it was permanently distorted under the repeated pressure operation and likewise produced products which were imperfect.

In practicing my invention, I employ a hard rubber composition which is Well known in the art as comprising rubber, a filler and a vulcanizing ingredient which is ground, thoroughly fixed and formed into unvulcanized sheets M. A plurality of the sheets l4, preferably of a thickness less than one quarter of an inch, are mounted together as shown in Fig. 1 and are provided with a reinforcing member such as a screen l5 between the layers as shown in the figures.

The purpose of the screen is to prevent the shrinking of the material due to repeated heating or ageing and it is to be understood that an entire metal backing may be substituted for the screen in case heat is to be applied to the dies when in service. The metal die member I?! is first constructed, having a surface machined inwardly thereof conforming to the outer surface of the finished product It]. The surface of the die is disposed adjacent to the plurality of unvulcanized rubber sheets i 4 and placed in a steam press (not shown) wherein heat and pressure are applied to the die member [2 and the layers of sheets 14. The pressure employed is substantially 350 pounds per square inch while a temperature of 300 degrees F. was found to be sufficient to completely vulcanize the rubber sheets into a solid homeogeneous structure or die l3.

After the sheets of rubber have been thoroughly heated to this temperature under the application of pressure, the heat is then shut ofi and the pressure retained until the vulcanized material has cooled below a temperature at which shrinkage would occur. The die and the rubber member is then removed from the press and the material l6, about the edges of the projecting portions H of the molded member, is then machined away to provide clearance between the die surfaces for receiving the sheet ID to be formed, as illustrated in Fig. 3. The mated memi ber, thus constructed of hard rubber composition,

has a slight resiliency at every portion of its mass to which its longevity is contributed.

In Fig. 3 I have disclosed the pair of dies l2 and I3 in their finished form with a sheet of cardboard lii placed therebetween and subjected to a pressure sufficient to form the cardboard into the shape of the forming surfaces of the dies.

When a more intricately formed product is desired, such for example as that shown in Fig. 7, a greater saving in time and cost ensues when employing a die as above constructed. In Fig 5 and Fig. 6 I have shown the method employed in constructing such a die wherein the arrangement of the sheets of material conform to the raised or indented portion of the master die I8, with pieces thereof laid in the proper position relative thereto.

When raised portions 25 are provided on the die l G a sheet l 4 is cut into three pieces and spaced from each other to provide channels 2| which are directly opposite to the raised portions 2 When indentations 22 are provided in the die [8, strips 23 of the material are placed on the top of the layers l4 directly opposite to the indentations.

When the die is firmly pressed onto the plurality of layers the projections 20 register with the channels 2| and cause the walls thereof to fiow into a shape substantially that of the projections as shown in Fig. 6. Similarly the material of the strips 23, register in the indentations 22 and flow under pressure to completely fill the indentations as shown in the figure. Heat is applied during the pressing operation, as indicated above, and the material is thereby firmly vulcanized into a homeogeneous mass which becomes hard upon being cooled and which is provided with a surface which is congruent with the surface of the steel die l8.

When the raised surface 24 of the finished product 25 is to be embossed in a manner somewhat similar to that shown in Fig. 7, I prefer to have the steel die provided with the recesses or indentations 22 having the negative contour of the bosses 25 thereon. It is considerably cheaper to cut away the surface of the recess to provide indentations, than it is to provide a relieved portion of the die with raised surfaces the exact shape of the bosses 26. Accordingly, the recesses 22 are provided with indentations, conforming in shape to a negative of the bosses 26 and the body portion is provided With an indentation which is a negative of the figure 27. When the die l8 is pressed into the material, the raised portion 24 will be provided with the embossing 26 in relief and the body portion will be provided with the relieved embossing 27.

It is to be understood that sheets of other materials such as metal of a gauge less than of the thickness of the cardboard, may readily be formed between the die members thus provided. It is to be further understood that several sets of dies may be formed from a single master die, the mated or composite die being utilized for forming dies from the sheet material in the manner above indicated which will be similar to the original master dies. This construction further reduces the cost of a product, a large number of which are formed by a set of dies, as any number of such sets of dies may be made from a single master die member.

It will thus be seen that I have provided a die, 40

for embossing thin sheet material under pressure, which is formed by a master die from a material which has a longevity at least equal to that of a metal die. When the master die and the composite die formed therefrom are both employed as master dies any number of such sets of dies may be constructed from a single master die cut by hand.

While I have described and illustrated but two embodiments of my invention, it will be apparent to anyone skilled in the art that many changes, omissions, additions and substitutions may be made therein without departing from the spirit and scope of my invention as set forth in the accompanying claims.

I claim as my invention:

1. The method of constructing a pair of dies for forminga sheet of material into a predetermined shape which includes, the steps, of constructing one of the dies from a solid material having one surface conforming to said predetermined shape, of pressing said surface into a pliable material, of hardening said material, and of machining at least one of said elements of the die at the sides of the matable male and female portions to provide side clearance therebetween for the sheet.

2. The method of constructing a pair of dies for forming a sheet into a predetermined shape which includes the steps of constructing one of the dies from a solid material having one surface conforming to the aforesaid predetermined shape, of pressing said surface into a vulcanizable material, of vulcanizing said material while pressed by said surface, of vulcanizing said material to a rigid member, and of machining at least one of the dies at the sides of the matable male and female portions to effect a side clearance for receiving said sheet to be formed.

3. The method of constructing a pair of dies for forming a sheet of material into a predetermined shape which includes the steps, of constructing one of the dies from a solid member having one surface machined to conform to the aforementioned predetermined shape, of pressing said surface into an unvulcanized rubber material, of vulcanizing said material to a metal member to harden said material and to effect a rigid mated die element, and of machining at least one of said elements of the die at the sides of the matable male and female portions to provide side clearance for the sheet to be formed therebetween.

4. The method of constructing a pair of dies for forming a sheet of material into predetermined shapewhich includes the steps, of constructing one of the dies from a solid member having one surface machined to conform to the aforesaid predetermined shape, of pressing said surface into a plurality of layers of unvulcanized sheets of hard rubber material, of reinforcing said sheets, of vulcanizing said material While pressed by said surface, of cooling said material While pressed, and of machining at least one of said die elements at the sides of the matable male and female portions to effect a side clearance for receiving the 

